Porous catalyst washcoats

ABSTRACT

Catalyst washcoats with improved porosity and methods for making the washcoats are provided. The process comprises incorporation of an oil-in-water macroemulsion into the catalyst slurry prior to washcoating the carrier substrate, and calcining the washcoated carrier substrate to remove the oil-in-water macroemulsion. Also provided are catalyst articles comprising the washcoat and methods for abatement of exhaust gas emissions.

TECHNICAL FIELD

The invention relates to the field of catalyst washcoats and methods ofmaking catalyst washcoats. The invention also relates to catalystarticles coated with catalyst washcoats and methods for using thecatalyst articles for exhaust gas abatement.

BACKGROUND

In catalytic converters, a substrate is coated with a catalyst washcoatwhich contains the catalyst(s), catalyst supports, etc. High surfacearea is desirable in the washcoat to maximize catalysis. Other desirablewashcoat properties include thermal stability and a pore sizedistribution that allows high flow-through of gases to optimize contactwith the catalysts). In particular, use of fine particles in thewashcoat can result in a dense washcoat layer with reduced porosity andimpaired catalytic activity. In addition, dense nonporous washcoats maycrack during heat treatment resulting in lack of adhesion andcompromised durability.

There exists a need for catalyst washcoats with increased porosity,particularly catalyst washcoats that can be produced using simplemethods that are easily incorporated into the manufacture of catalystarticles such as catalytic converters. The present invention addressesthese needs.

SUMMARY

In one aspect, the invention relates to methods for increasing porosityin a catalyst washcoat. The methods comprise incorporating an aqueousoil-in-water (O/W) macroemulsion into a washcoat slurry containing thecatalyst(s) and other components of the washcoat, washcoating a carriersubstrate with the washcoat slurry, and calcining the washcoated carriersubstrate to remove the macroemulsion. Upon calcination, the oil, water,and other organic components of the macroemulsion are burned off, andthe oil macroparticles of the emulsion leave behind macropores in thecalcined washcoat. In one or more embodiments, the O/W macroemulsioncomprises an oil or other hydrophobic hydrocarbon, water or otheraqueous phase, and a surfactant having a hydrophile-lipophile balance(HLB) of 8-16 or 10-12. In one or more specific embodiments, the O/Wmacroemulsion comprises mineral oil, a nonionic surfactant HLB 10-12,and water.

In a second aspect, the invention relates to catalyst washcoatcompositions, wherein at least about 30% (i.e., 30-100%) of pores withinthe catalyst washcoat are about 15 μm-100 μm in size in at least onedimension or about 15 μm-100 μm in diameter if the pore is substantiallyspherical. In certain specific embodiments, at least about 70% (i.e.,70-100%) of the pores within the catalyst washcoat are about 15 μm-100μm in size in at least one dimension or in diameter if the pore issubstantially spherical. In further specific embodiments, at least about30% (i.e., 30-100%), about 60% (i.e., 60-100%), or at least about 70%(i.e., 70-100%) of the pores within the catalyst washcoat are about 15μm-50 μm in size in at least one dimension or in diameter if the pore issubstantially spherical.

In a particular embodiment, catalysts and other solid components of thecatalyst washcoat of the catalyst article can be selected for use inabatement of exhaust gas emissions. The emissions to be abated may be ofany type for which a suitable catalyst is available. The catalyst shouldbe capable of formulation as a washcoat slurry. For example, in certainspecific embodiments, the catalyst washcoat may comprise catalysts foroxidation of hydrocarbons, carbon monoxide, and nitrogen oxides (NOx) ingasoline and diesel engines. In alternative embodiments, the catalystwashcoat may comprise catalysts for storage reduction of NOx (NSRcatalysts) or catalysts for selective catalytic reduction of NOx tonitrogen (SCR catalysts) in exhaust gas emissions. In further specificembodiments, the catalyst components of the washcoat may be selected forabatement of exhaust gas emissions from industrial processes, such asmethyl bromide, carbon monoxide, benzene, and volatile organiccomponents (VOCs) including methane, toluene, xylene, acetic acid,methanol, etc.

In a further aspect, the invention relates to catalyst articles for usein abatement of exhaust gas emissions, wherein the catalyst articlecomprises a carrier substrate coated with the catalyst washcoataccording to any of the catalyst washcoat embodiments and aspectsdescribed above. In one or more embodiments, the carrier substrate is aceramic or metal structure having a honeycomb structure in whichparallel gas flow passages extend through the structure from a fluidinlet to a fluid outlet. The walls of the passages are coated with thecatalyst washcoat so that exhaust gases flowing through the passagescontact the catalyst washcoat. The carrier substrate may be a wall flowmonolith which has a plurality of longitudinally extending passages. Thepassages include inlet passages that have an open inlet end and a closedoutlet end, and outlet passages that have a closed inlet end and an openoutlet end. The walls forming the passages are porous, allowing exhaustgas to cross over from an inlet passage to an outlet passage to exit themonolith, thereby flowing through the catalyst washcoat on the walls. Inone or more embodiments, the ceramic or metal carrier substrate may bein the form of pellets, corrugated sheets or in monolithic form coatedwith the catalyst washcoat.

In yet a further aspect, the invention relates to methods for abatementof exhaust gas emissions using the catalyst articles according to any ofthe foregoing aspects and embodiments of the invention. The exhaust gascontaining the emissions to be abated is contacted with the catalystarticle such that the catalyst washcoat contacts the exhaust gas in amanner effective to produce the desired catalytic conversion and abatethe selected component or components of the exhaust gas.

In still another aspect, the invention relates to systems for abatementof exhaust gas emissions, wherein the system includes a catalyst articleaccording to any of the foregoing embodiments and aspects. The systemcan include a catalyst article according to any of the embodiments andaspects described above, and one or more of a soot filter, a catalyzedsoot filter, and/or additional conventional catalyst articles asdesired. The components of the system for abatement of exhaust gasemissions are in fluid flow contact with the source of the exhaust gasand with each other. In certain embodiments, the exhaust gas streamflows from its source into sequential contact with the catalyst articleof the invention and the other components of the system to achieveabatement of exhaust gas emissions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an X-ray microtomography (XMT) image of a honeycomb carriersubstrate washcoated with a conventional catalyst washcoat and calcined,i.e., a catalyst washcoat that was not prepared with a macroemulsion.

FIG. 1B is an X-ray microtomography (XMT) image of a honeycomb carriersubstrate washcoated with a catalyst washcoat according to the inventionand calcined, i.e., a catalyst washcoat that was prepared with amacroemulsion.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the invention, it isto be understood that the invention is not limited to the details ofconstruction or process steps set forth in the following description.The invention is capable of other embodiments and of being practiced orbeing carried out in various ways.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe invention. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the invention.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

As used herein, the term “within the catalyst washcoat” in connectionwith the pores of the washcoat refers to pores of the washcoat that arebetween the solid particles of the washcoat composition. The solidparticles of the washcoat composition include the catalyst, refractorymetal oxide supports, oxygen storage components, promoters, binders andthe like. These solid particles may have an internal pore system in theparticle itself. The pores of a support particle are used to impregnatecatalysts and other components into the solid particle. The pores of thesolid particles of the washcoat composition are typically micropores,which have dimensions in the nanometer range or at most 1-2 μm. Incontrast, the pores “within the catalyst washcoat” of the invention arebetween the solid particles of the washcoat and are macropores whichhave a size of at least 15 μm in at least one dimension.

As used herein, the terms “macropore” and “macroporous” refer to amaterial having pores with a size equal to or greater than about 15 μmin at least one dimension. If the macropore is substantially spherical,the diameter of the macropore is equal to or greater than about 15 μm.The terms “micropore” and “microporous” refer to a material having poreswith a size of less than about 10 μm in at least one dimension. If themicropore is substantially spherical, the diameter of the micropore isless than about 10 μm.

Similarly, as used herein, the term “macroparticle” with respect to anemulsion refers to the oil phase particles of the emulsion which have adiameter equal to or greater than about 15 μm. The term “microparticle”with respect to an emulsion refers to the oil phase particles of theemulsion which have a diameter of less than about 10 μm.

As used herein, the term “washcoat” has its usual meaning in the art ofa thin, adherent coating of a catalytic or other material applied to asubstrate carrier material, such as a honeycomb-type substrate or wiremesh, which is contacted by the gas stream being treated to effectremoval of exhaust gas pollutants. A washcoat is formed by preparing aslurry containing a specified solids content of catalysts and/orcarriers in a liquid vehicle, which is then coated onto a substrate anddried to provide a washcoat layer.

As used herein, the term “support” with respect to a catalyst refers toa material that receives platinum group metals, stabilizers, promoters,binders, and the like through association, dispersion, impregnation, orother suitable methods. Examples of supports include, but are notlimited to, refractory metal oxides, high surface area refractory metaloxides and materials containing oxygen storage components. High surfacearea refractory metal oxide supports include activated compoundsselected from the group consisting of alumina, alumina-zirconia,alumina-ceria-zirconia, lanthana-alumina, lanthana-zirconia-alumina,baria-alumina, baria lanthana-alumina, baria lanthana-neodymia alumina,and alumina-ceria. Examples of materials containing oxygen storagecomponents include, but are not limited to, ceria-zirconia,ceria-zirconia-lanthana, zirconia-praseodymia, yttria-zirconia,zirconia-neodymia and zirconia-lanthana. In certain embodiments, thesupport comprises bulk rare earth metal oxide such as bulk ceria havinga nominal rare earth metal content of 100% (i.e., >99% purity).

As used herein, the terms “abate,” “abatement” and the like, withrespect to treatment of exhaust gas streams, refer to removal of orreduction in pollutants and/or toxic components in the exhaust gas.

In a first aspect, the invention relates to methods for increasingporosity in a catalyst washcoat. The methods comprise incorporating anaqueous oil-in-water (O/W) macroemulsion into a washcoat slurrycontaining the catalyst(s) and other components of the washcoat,washcoating a carrier substrate with the washcoat slurry, and calciningthe washcoated carrier substrate to remove the macroemulsion. Uponcalcination, the oil, water, and other organic components of themacroemulsion are burned off, and the oil macroparticles of the emulsionleave behind macropores in the calcined washcoat. To make themacroemulsion, a surfactant is added to the oil phase while stirring toproduce a dispersion. The aqueous phase is then added slowly to thedispersion with an increased speed of stirring so that the mixture isturbulent. Vigorous, turbulent stifling is continued until sufficientaqueous phase has been added to produce the desired O/W emulsion, andfor an additional time as necessary to produce a stable O/Wmacroemulsion. To obtain the stable O/W macroemulsion, the ratio ofaqueous phase:oil:surfactant is selected such that about 30-100% of theoil particles are equal to or greater than about 15 μm in diameter inthe macroemulsion.

The O/W macroemulsion is then incorporated into the catalyst washcoatslurry with stifling. The catalyst washcoat slurry may be any catalystwashcoat slurry known in the art, as determined by the intended end-use.In this manner, the aqueous phase of the O/W macroemulsion isincorporated into the aqueous catalyst washcoat slurry, and the oilmacroparticles form droplets between the solid particles of the catalystwashcoat slurry. The catalyst washcoat slurry is then applied to acarrier substrate to form a layer on the surface of the carriersubstrate, and calcined using methods customary in the field. The timeand temperature of calcining are selected so that the oil components ofthe O/W macroemulsion (and the aqueous components of the washcoatslurry) are burned off. This creates pores within the calcined washcoatthat approximately represent the size and number of the oil particles inthe O/W macroemulsion. That is, because the oil particles of themacroemulsion include a proportion of macroparticles, a similarproportion of macropores are formed within the calcined washcoat. Thenumber and size of macropores in the calcined washcoat can be adjustedby selection of the oil and the surfactant (which affects oil particlesize distribution) and by the amount of O/W macroemulsion incorporatedinto the catalyst washcoat slurry (which affects the number of poresformed).

The oil phase of the O/W macroemulsion may be any oil or otherhydrocarbon suitable for forming a macroemulsion, or mixtures thereof.The carbon chain length of the oil or other hydrocarbon is related tothe particle size in the emulsion, with larger molecules (i.e., longercarbon chain lengths) producing larger oil particles. However, oilshaving shorter carbon chain lengths are more easily removed bycalcining. The practitioner can therefore select an oil or otherhydrocarbon of appropriate carbon chain length to achieve the desiredproportion of macroparticles in the macroemulsion, and can adjust thetemperature and time of calcining to remove it from the catalystwashcoat. In one or more embodiments, the oil or other hydrocarbon has acarbon chain length of C6-C40, C10-C40, or is a mixture of hydrocarbonshaving carbon chain lengths in this range. By way of example, theoil/hydrocarbon phase may be mineral oil (a mixture of C15-C40 alkanes),hexane (C6), or mixtures thereof.

The surfactant of the O/W macroemulsion may be any surfactant known inthe art for producing O/W emulsions. Anionic, cationic, nonionic andamphoteric surfactants can be used. In one or more embodiments, thesurfactant is a nonionic surfactant having an HLB of 8-16 or 10-12. Useof nonionic surfactants in catalyst applications has the advantage ofavoiding introduction of contaminating species such as Na, Cl, Br and Sinto the catalyst washcoat, which may compromise catalyst activity. Thechain length of the surfactant affects the size of the oil particles ofthe emulsion, with longer chain lengths supporting formation of largeroil particles. The practitioner can therefore select a surfactant ofappropriate chain length to achieve the desired proportion of oilmacroparticles in the macroemulsion. By way of example, suitablesurfactants include octylphenol ethoxylates (e.g., TRITON Xsurfactants), secondary alcohol ethoxylates (e.g., TERGITOL 15-S Seriessurfactants), branched secondary alcohol ethyoxylates (e.g., TERGITOLTMN Series surfactants), diethoxylates of tallow amine (e.g., SURFONIC TSeries surfactants), ethoxylates of linear primary alcohols (e.g.,SURFONIC L Series surfactants), and polyoxyethylene surfactants (e.g.,TWEEN surfactants). In specific non-limiting examples, the surfactant isa nonionic surfactant selected from the group consisting of TRITON X-45(HLB 9.8), TRITON X-114 (HLB 12.3), TERGITOL 15-S-5 (HLB 10.5), TERGITOL15-S-7 (HLB 12.1), TERGITOL 15-S-12 (HLB 14.5), TERGITOL TMN-6 (HLB13.1), SURFONIC T-20 (HLB 15.3), and SURFONIC L24-22 (HLB 16.6). Ingeneral, surfactants with HLB 10-12 are most suitable for macroemulsionsutilizing mineral oil. The most suitable HLB for the surfactant dependson the particular oil used in the macroemulsion.

The aqueous phase of the O/W macroemulsion is typically water, such asdeionized water.

In the O/W macroemulsion, the oil or other hydrocarbon, aqueous phaseand surfactant are present in proportions that promote formation of astable O/W macroemulsion. The aqueous phase is typically in excess, andthe amount of surfactant is selected based on the amount of oil suchthat oil particles of the desired size are produced and stabilized inthe aqueous phase (i.e., the amount of surfactant is an amountsufficient to stably emulsify the amount of oil that is present). In oneor more embodiments, the 0/W macroemulsion is prepared so as to containat least about 30% (i.e., 30-100%) oil phase particles about 15 μm-100μm in diameter. In certain specific embodiments, at least about 70%(i.e., 70-100%) of the oil phase particles are about 15 μm-100 μm indiameter. In further specific embodiments, at least about 30% (i.e.,30-100%), at least about 60% (i.e., 60-100%), or at least about 70%(i.e., 70-100%) of the oil phase particles are about 15 μm-50 μm indiameter.

In one or more embodiments, the O/W macroemulsion comprises 58-62%water, 30-40% mineral oil, and 4-6% TRITON X-45 or TRITON X-114. In oneor more further embodiments, the O/W macroemulsion comprises about 60%DI water, about 35% mineral oil, and about 5% TRITON X-45.

The catalyst washcoat slurry may be any catalyst washcoat slurry knownin the art that is suitable for washcoating a carrier substrate. Theslurry may comprise one or more selected catalysts, including preciousgroup metal catalysts, base metal catalysts, SCR catalysts, and/orzeolites. The one or more catalysts may be impregnated on supportmaterials, including refractory metal oxides (e.g., alumina, rare-earthmetal oxides, zirconia, titania and combinations thereof) or oxygenstorage components such as ceria. The washcoat slurry may furtherinclude other components of the catalyst washcoat, such as promoters andbinders.

The O/W macroemulsion is incorporated into the catalyst washcoat slurryin an amount selected to obtain the desired degree of macroporosity inthe calcined washcoat. The degree of macroporosity in the calcinedwashcoat is determined by the proportion of oil macroparticles in themacroemulsion as compared to microparticles, and the amount of O/Wmacroemulsion added to the catalyst washcoat slurry. In one or moreembodiments, the O/W macroemulsion constitutes about 2% to about 50% ofthe catalyst washcoat slurry. In other embodiments, the O/Wmacroemulsion constitutes about 2% to about 15% of the catalyst washcoatslurry. In further embodiments, the O/W macroemulsion constitutes about5% of the catalyst washcoat slurry.

After mixing the O/W macroemulsion with the catalyst washcoat slurry,the catalyst washcoat is formed on the carrier substrate usingconventional methods such as dipping the carrier in the catalystwashcoat slurry. The carrier substrate may be any of the known carriersubstrates and is selected according to the intended end-use of thecatalyst article. For example, the carrier substrate may be ceramic ormetal. The carrier substrate may be a monolithic substrate of thehoneycomb type having fine, parallel gas flow passages extendingtherethrough from an inlet or an outlet face of the substrate such thatpassages are open to fluid flow therethrough. The passages areessentially straight paths from their fluid inlet to their fluid outlet,and are defined by walls on which the catalytic material is coated as awashcoat so that the gases flowing through the passages contact thecatalytic material. Wall flow carrier substrates are particularly usefulas carrier substrates for the macroporous washcoats of the invention, asthe walls of the parallel passages of these substrates are porous sothat the exhaust gas flows through the washcoat and the walls of thepassages into an adjacent passage before exiting the monolith. Ceramicsubstrates may be made of any suitable refractory material, e.g.,cordierite, cordierite-α-alumina, silicon nitride, zircon mullite,spodumene, alumina-silica-magnesia, zircon silicate, sillimanite, amagnesium silicate, zircon, petalite, α-alumina, an aluminosilicate andthe like. Metallic substrates may be composed of one or more metals ormetal alloys, and may be in various shapes such as pellets, corrugatedsheets or monolithic form. Specific examples of metallic substratesinclude the heat-resistant, base-metal alloys, especially those in whichiron is a substantial or major component. Such alloys may contain one ormore of nickel, chromium, and aluminum.

The washcoated carrier substrate is then calcined using a time andtemperature sufficient to both thermally treat the catalyst and removethe components of the O/W macroemulsion. Temperatures between 300° C.and 700° C. for 1 hr. to 4 hr. in air are generally sufficient for thispurpose. In one or more embodiments, the carrier substrate washcoatedwith the catalyst washcoat/O/W macroemulsion is calcined for 1-2 hr. at400-500° C.

The above processes produce a catalyst washcoat composition on thecarrier substrate (the catalyst article) wherein at least about 30%(i.e., 30-100%) of pores within the catalyst washcoat are about 15μm-100 μm in size in at least one dimension or about 15 μm-100 μm indiameter. In certain specific embodiments, at least about 70% (i.e.,70-100%) of the pores within the catalyst washcoat are about 15 μm-100μm in size in at least one dimension or in diameter. In further specificembodiments, at least about 30% (i.e., 30-100%), about 60% (i.e.,60-100%), or at least about 70% (i.e., 70-100%) of the pores within thecatalyst washcoat are about 15 μm-50 μm in size in at least onedimension or in diameter.

The catalyst article with the macroporous catalyst washcoat is usefulfor abatement of exhaust gas emissions. The emissions to be abated maybe of any type for which a suitable catalyst is available, provided thecatalyst can be formulated as a washcoat slurry. For example, in certainspecific embodiments, the washcoat of the catalyst article may comprisecatalysts for oxidation of hydrocarbons, carbon monoxide, and nitrogenoxides (NOx) in the exhaust streams of gasoline and diesel engines. Inalternative embodiments, the washcoat of the catalyst article maycomprise catalysts for storage reduction of NOx (NSR catalysts) orcatalysts for selective catalytic reduction of NOx to nitrogen (SCRcatalysts) in the exhaust streams of gasoline and diesel engines. Infurther specific embodiments, the washcoat of the catalyst article maycomprise catalysts for abatement of exhaust gas emissions fromindustrial processes, such as methyl bromide, carbon monoxide, benzene,and volatile organic components (VOCs) including methane, toluene,xylene, acetic acid, methanol, etc. The exhaust gases to be abated arecontacted with the catalyst article such that the catalyst washcoatcontacts the exhaust gas in a manner effective to produce the desiredcatalytic conversion and abate the selected component or components ofthe exhaust gases. Catalytic conversion of pollutants and toxins in theexhaust gases is improved by the macroporosity of the catalyst washcoatsof the invention due to improved flow-through and surface area contactwith the catalyst.

The catalyst article according to the invention may be included in asystem for abatement of exhaust gases. In addition to the catalystarticle of the invention, such systems may further include one or moreof a soot filter, a catalyzed soot filter, and additional conventionalcatalyst articles as desired. The components of the system for abatementof exhaust gas emissions are in fluid flow communication with the sourceof the exhaust gas and with each other such that the exhaust gas streamflows from its source into sequential contact with the catalyst articleof the invention and the other components of the system to achieveabatement of exhaust gas emissions.

EXAMPLE

An oil-in-water emulsion was prepared using the following materials:

Material Amount (g) Percent of Emulsion DI Water 27.5 61.11 Surfactant:Triton X-45 2.5 5.5 Mineral Oil 15 33.33

The mineral oil was weighed out in a glass beaker, and the surfactantwas added while stirring with a magnetic stir bar. The DI water wasweighed out in a separate beaker. The speed of stirring of theoil/surfactant mixture was increased so that turbulence formed a vortex.The water was slowly added dropwise to the oil/surfactant mixture untilall water was added, and mixing was continued for an additional 10minutes to obtain the O/W macroemulsion. Analysis of the particle sizedistribution of the O/W macroemulsion showed that it contained a minimumof about 30% of oil particles equal to or greater than about 15 μm indiameter.

The O/W emulsion was then incorporated into a catalyst slurry asfollows:

Material Amount (g) % of total slurry O/W emulsion 12.5 5.06 Slurry(Pd/Alumina + Rh/OSC) 234.58 94.94

The catalyst slurry was thoroughly mixed by shaking the container andmixing by hand. The emulsion was similarly mixed thoroughly, and addedin the specified amount to the slurry while mixing thoroughly.Cordierite carrier substrates were washcoated with the catalyst/O/Wemulsion slurry and calcined at 500° C. for 2 hrs.

For comparison, a catalyst slurry having the same composition wasprepared, but was not mixed with the O/W emulsion. This comparisonslurry was also washcoated on cordierite carrier substrates and calcinedat 500° C. for 2 hrs.

XMT images of the resulting washcoats are shown in FIG. 1A and FIG. 1B.FIG. 1A shows the washcoat without incorporation of the macroemulsion.The panel on the right side is a longitudinal section of the passages,where the washcoat is seen as lighter layers on each side of the darkerwalls of the parallel passages. The washcoat layers are thin and dense,with very little porosity. In contrast, FIG. 1B shows the washcoatprepared with the O/W macroemulsion. The washcoat layers are thicker andappear spongy, with a large number of pores in the macroporous sizerange.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It will be apparent to those skilled in the art thatvarious modifications and variations can be made to the method andapparatus of the present invention without departing from the spirit andscope of the invention. Thus, it is intended that the present inventioninclude modifications and variations that are within the scope of theappended claims and their equivalents.

1. A catalyst article comprising a catalyst washcoat on a carriersubstrate, wherein about 30%-100% of pores within the catalyst washcoatare about 15 μm-100 μm in size in at least one dimension.
 2. Thecatalyst article of claim 1, wherein about 70%-100% of the pores withinthe catalyst washcoat are about 15 μm-100 μm in size in at least onedimension.
 3. The catalyst article of claim 1, wherein about 70%-100% ofthe pores within the catalyst washcoat are about 15 μm-50 μm in size inat least one dimension.
 4. The catalyst article of claim 1, wherein thecarrier substrate is cordierite or metal.
 5. The catalyst article ofclaim 1, wherein the catalyst washcoat comprises a precious group metalcatalyst and/or a base metal catalyst.
 6. The catalyst article of claim5, wherein the precious group metal catalyst and/or base metal catalystis impregnated on a support material. 7-16. (canceled)
 17. A system forabatement of exhaust gas emissions comprising a source of exhaust gasesin fluid flow communication with a catalyst article according to claim1, and at least one of a soot filter, a catalyzed soot filter and asecond catalyst article in fluid flow communication with the catalystarticle.
 18. The system of claim 17, wherein the carrier substrate is aceramic or metal honeycomb substrate.
 19. The system of claim 18,wherein the carrier substrate is a flow-through monolithic substrate ora wall flow substrate.